Fix permissions as required for cron jobs

[GMDSantana]

The files under /etc/cron.d do not need to be executable, while the files under /etc/cron.hourly, /etc/cron.daily, /etc/cron.weekly and /etc/cron.monthly do, as they are run by run-parts command ( see: https://www.cyberciti.biz/cloud-computing/why-is-my-linux-unix-crontab-job-not-working/ )